Review: RSM Racing 80 MM throttle body
I installed the RSM Racing 80 mm throttle body on my 1998 Aurora with the 4.0 V8. I did this at the dyno and got some before and after results. I measured the TB and it seemed to measure 79.5 mm, not quite 80 mm. My stock TB seems to measure 76 mm. It's my understanding that they are supposed to be 75mm, but I'm not really sure. Also, the TB was also recently cleaned, so the comparison should be good with the new bored out TB. It was also 87 degrees for these runs, so it was much hotter than previous visits to the dyno to test other modifications when it was about 70 degrees. Here are the numbers:
Baseline runs: 191.1 HP, 205 torque
193.2 HP, 209.1 torque
The first baseline was not as strong, and I think it's because the engine was not up to full temp. After installing the throttle body, I had three runs that were essentially identical. I'm comparing the results to the better base line to be conservative.
New TB runs: 198.6 HP, (+5.4 peak HP - at wheels)
214.2 torque (+5.1 peak torque)
The gains were all over the curve which is really most important. Here is the comparison for various RPM's:
4200 rpm + 7.8 HP, + 9.6 torque
4400 + 5.8 HP, + 7.0 torque
4600 + 5.2 HP, + 5.9 torque
4800 + 6.5 HP, + 6.8 torque
5000 + 5.3 HP, + 5.7 torque
5200 + 5.4 HP, + 5.5 torque
5400 + 4.8 HP, + 4.7 torque
5600 + 4.7 HP, + 4.4 torque
5800 + 3.8 HP, + 3.5 torque
6000 + 4.7 HP, + 4.0 torque
The car seems to run just the same for regular driving with no negative affects. I'd recommend this modification - especially for the 4.6 caddy guys. It will probably help the 4.6 even more. This throttle body fits the 4.6 northstars as well. Just check out RSM Racing's web site.
When making this modification, it's important to go through the throttle position learn procedure. All you do is Turn the ignition switch to the ON position with the engine not running, wait 30 seconds, turn the ignition switch to the LOCK position, and wait another 30 seconds. That's it.
Here are the dyno graphs.
Here is a picture of the 80 mm bored out throttle body.
Just a few comments from Greg:
1. The stock TB is supposed to be 75 mm and the bored TB is supposed to be 80 mm. However, RSM racing says that the bored TB ends up being anywhere between 79 and 80 depending on the core they get. The stock TB ranges from 74 to 76 mm. So, my results should be a minimum gain really. I was experiencing a gain of only 3.5 mm over stock. Most others will see a gain of 5 mm.
2. The 4.6 obviously breaths harder than a 4.0 therefore the stock TB is going to be more of a restriction on a 4.6. The 4.6 should see even more gain than a 4.0.
3. The only other mod I have going right now is a modified air box (gutted it as shown on caddyinfo.com) and I use a K&N filter. That's it. In the future, I hope to add the Corsa exhaust.
4. The port through the TB is substantially smaller than the rest of the intake ducting. It's a restriction a simple as that. I'm sure they are made as large as can be for getting reliable mass produced cast parts.
5. A restriction is a restriction no matter what is in front or behind it. When looking at a modification to help air flow, all the restrictions in the line basically add up. Does the TB show more of a gain because I have a K&N filter? - Sure a little, but it would still show a gain with paper. After all, I got a nice gain at the dyno from the K&N and air box mod with the stock TB. An exception to this would be if air flow was extremely restriced up or down-stream of a mod. Example - your filter is thicker than a chunky peanut butter sandwhich with dirt and bugs, or the converter is fouled and plugged.
6. I wouldn't assume the engineers put too much thought into the intake and exhaust all the time. The stock air box is very restrictive and pushes all the air through a small portion of the filter. If they want a quiet air box, they could have double walled it on the outside instead of putting a liner on the inside that restrics flow. It really seems that not a lot of thought goes into the intake and exhaust as it regards to performance. They just choke the thing off to keep it quiet.
7. Oh yeah, If you do this, GET THE TB MOUNTING PLATE! It's between the TB and manifold. You can bore this too and probably taper the exit to match the manifold. RSM will do this as well and indicated that this must be done by hand - probably because of the tapering. If you are really nuts, I guess you can get another manifold and bore that out too so the whole thing is bigger from TB to the manifold. When you call a junk yard, make sure you get the TB AND the mounting plate just after it. Otherwise you end up with a bigger TB mated to a smaller bore plate (that's what I have now). So even more gains are possible if you match port everything.Here is an image of the ported Throttle body and the stock mounting:
Bruce, here are nice pictures of the throttle body mounting plate job that should go with any larger throttle body improvement. You can see what a nice job RSM did matching the mounting plate to the throttle body.
These were done separately and the plate had to be done by hand due to its angle.
One picture also shows the larger 80 mm throttle body bolted to the original mounting plate (the way I had it for the dyno tests) and you can see the bump caused by the smaller stock mounting plate.
If increasing the TB from approximately 75 mm to 80 mm made a nice increase in power, then removing the additional 2 mm obstruction from the mounting plate should help a bit too. It also matches the intake manifold opening exactly now since it is 80 mm stock.
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